Thank you! That means a lot to me.
I've had the same saga with my newly cycled 20L future blackwater tank that was for my Betta given to me by a client in a 2.5 gallon. I'm a pet sitter (we do fish, too, BTW. So sorry about Val
I always tell people you cannot trust friends and family for the most part. They don't have the experience and judgement to know what they don't know and OFTENTIMES they think they know better. Usually they do something COMPLETELY ridiculous or wrong you'd never dream of....leaving you wondering "WHAT the HECK were they THINKING!?". One time a client had a neighbor feed her lovebird. Instead of using HER FOOD, the idiot brought INTO HER HOME his large sized wild bird sunflower seed which a small parrot cannot even crack open and the poor bird died of starvation.)
Anyway....I acclimated him in the 20L and was all excited....and the ph matched THAT DAY 7.0....in but then realized my PH was bouncing so he went "back" into a 5.5 gallon where I can control the parameters much better. The prior owner used a certain bottled water with a high ph, too, so that's what he was used to.
My tap PH is 8.0! (the same as his former bottled water)....But I used Fluval Stratum which brings it down to VERY VERY low around 6.4 if that. AND some botanical to make matters worse LOL. From Tannin Aquatics...very nice BTW but DON'T ORDER ANY LOL.
So the challenge is what the heck do I do with water changes? I can't dump a bunch of 8.0 into a 6.4 environment.
Been all over the place during the learning curve.
Started with Eco Complete but had a HUGE high ph. Removed that and replaced with Fluval Stratum (ugh). THEN I had attached plants to (and used for hardscaping) a bunch of Seiryu Stone THEN learned it raises PH. So I had low ph Stratum competing with the stone.
I just added a very large seiryu stone back in but I don't like the idea of that because it's sort of artificially changing the ph and what happens when it all levels out if it ever does.
Sigh LOL. I've been thinking about changing substrates once more but still don't know what to do about this tap water 8.0. I guess I assumed the 8.0 combined with the Stratum 6.5 would "average out" to 7.0.
Sort of hoping it still does but what about water changes!?
Ironically just before you posted about aeration, I had put a new air stone in there just to see if I could get the tank to adjust faster - never thinking it would RAISE the PH again hahaha. Not too bright of me considering that air stone would HAVE TO GO once the Betta went back in.
Anyway, I think it's all the woods, plants and uncertainty of a new tank, not whether it's small or large so don't feel bad!
I think this betta is going to have to live in his nice little 5G and the 20L I set up will just have to be for a tank of fish who LOVE 8.0 with a new neutral substrate!!
Probably a rookie mistake worrying more about the cycling than forethought about the simple yet big problem of PH!
The entire thing started with inspiration from this youTube guy who did a beautiful blackwater tank for one betta with the same substrate and plants. But he never mentioned his PH and I never asked facepalm.
Also ironic I used to be a pet store owner and never had all this nonsense with 20 tanks of fish! WTH LOL.